At the heart of evolutionary theory is the basic idea that life has existed for billions of years and has changed over time.

Overwhelming evidence supports this fact. Scientists continue to argue about details of evolution, but the question of whether life has a long history or not was answered in the affirmative at least two centuries ago.

The history of living things is documented through multiple lines of evidence that converge to tell the story of life through time. In this section, we will explore the lines of evidence that are used to reconstruct this story.